If a crappy masker was doing the prep when I did autobody and had overspray on glass, I always stuck with razorblades. (just keep blade clean, wipe after each pass onto a damp rag).
Enough about me, lets get to the thread. I've used fine grade steel wool to clean window glass, do
not use on mirror glass. As with any new adventure, test spots first
on a side note, fine grade steel wool works great with chrome. (test small section, just to make sure, like anything)
After the glass is all contaminate free, I like to hit it up with some PP.